HONG KONG/SINGAPORE, May 14 (Reuters) - Standard Chartered plc is seeking buyers for its Hong Kong pension business valued at about $350 million in a deal that would also involve a 15-year distribution agreement with the new owner, people with knowledge of the matter told Reuters.

Suitors including Prudential plc, Principal Financial Group, Sunlife Financial Inc, Metlife Inc and Manulife Financial Corp are expected to take part in the auction, the people added.

Any deal would mark Standard Chartered's second sale of a Hong Kong business in less than six months and comes as newly appointed Chief Executive Bill Winters is expected to overhaul the Asia-focused lender which has faced a prolonged slump in profits and regulatory fines.

The sale is not part of Standard Chartered's restructuring but was aimed at offering better services to clients, two sources said.

Standard Chartered and all other companies the sources said were potential bidders declined to comment on the matter. The sources declined to be identified as the discussions are confidential.

The bank's possible exit also marks consolidation in Hong Kong's pension market, which is one of the world's least developed but where retirement savings is emerging as a new opportunity for insurers due to a rapidly ageing population, with a higher life expectancy, in the Asian financial hub.

Retirement savings accounted for just 40 percent of Hong Kong's GDP, compared with 101 percent in Australia, 84 percent in Canada and 62 percent in Japan, according to a 2013 study by consultants Tower Watsons.

Last November, French insurer AXA SA sold its Hong Kong pension business to Principal Financial for $335 million.. (Additional reporting by Deena Yao; Reporting by Denny Thomas and Saeed Azhar; Editing by Miral Fahmy)